Oblique illuminator for inspecting manufactured substrates

ABSTRACT

One embodiment relates to an oblique illuminator. The oblique illuminator includes a light source emitting a light beam, a first reflective surface, and a second reflective surface. The first reflective surface has a convex cylindrical shape with a projected parabolic profile along the non-powered direction which is configured to reflect the light beam from the light source and which defines a focal line. The second reflective surface has a concave cylindrical shape with a projected elliptical profile which is configured to reflect the light beam from the first reflective surface and which defines first and second focal lines. The focal line of the first reflective surface is coincident with the first focal line of the second reflective surface. The first and second focal lines of the second reflective surface may be a same line in which case the elliptical curvature is a projected spherical profile. Other embodiments, aspects and features are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of provisional U.S. PatentApplication No. 61/369,625, filed Jul. 30, 2010 by inventors Shiyu ZHANGet al., the disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates to apparatus and methods for providingillumination. More particularly, the present disclosure relates toapparatus and methods for providing oblique illumination for use, forexample, in the inspection of manufactured substrates.

2. Description of the Background Art

Inspection processes are used at various steps during a semiconductormanufacturing process to promote higher yield. However, as thedimensions of semiconductor devices decrease, the detection of defectsof decreasing size has become necessary to avoid unwanted manufacturingerrors in the devices.

One way to improve the detection of such very small defects is toincrease the sensitivity of an optical inspection system. Thesensitivity of an optical inspection system may be increased, forexample, by using oblique illumination, instead of normal illumination.

SUMMARY

One embodiment relates to an oblique illuminator. The obliqueilluminator includes a light source emitting a light beam, a firstreflective surface, and a second reflective surface. The firstreflective surface has a convex cylindrical shape with a projectedparabolic profile along the non-powered direction of the cylinder whichis configured to reflect the light beam from the light source and whichdefines a virtual focal line. The first reflecting surface with such aprofile may be referred to as a parabolic cylindrical reflectingsurface. The second reflective surface has a concave cylindrical shapewith projected elliptical profile which is configured to reflect thelight beam from the first reflective surface and which defines first andsecond focal lines. The virtual focal line of the first reflectivesurface is coincident with the first focal line of the second reflectivesurface. The first and second focal lines of the second reflectivesurface may be a same line in which case the projected ellipticalprofile is a spherical one.

Another embodiment relates to a method of illuminating a line segment ona surface of a target substrate. A light beam is emitted from a lightsource. The light beam is reflected from a first reflective surface. Thefirst reflective surface has a convex cylindrical shape with a projectedparabolic profile which defines a focal line. The light beam is furtherreflected from a second reflective surface. The second reflectivesurface has a concave cylindrical shape with a projected ellipticalprofile which defines first and second focal lines. The virtual focalline of the first reflective surface is coincident with the first focalline of the second reflective surface.

Another embodiment relates to an apparatus for inspecting a targetsubstrate. The apparatus includes an oblique illuminator and a detector.The oblique illuminator includes a light source emitting a light beam, afirst reflective surface, and a second reflective surface. The firstreflective surface has a convex cylindrical shape with a projectedparabolic profile which is configured to reflect the light beam from thelight source and which defines a focal line. The second reflectivesurface has a concave cylindrical shape with a projected ellipticalprofile which is configured to reflect the light beam from the firstreflective surface and which defines first and second focal lines. Thefocal line of the first reflective surface is coincident with the firstfocal line of the second reflective surface, and the second focal lineof the second reflective surface lies on a surface of the targetsubstrate such that a line segment is illuminated on the surface of thetarget substrate.

One example of the target substrate may be a semiconductor wafer; andthe manufactured substrates may refer to patterned wafers.

Other embodiments, aspects and features are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical system layout of a previous oblique illuminator foruse in inspecting manufactured substrates.

FIG. 2 shows ray fan plots of the oblique illuminator of FIG. 1 with arelatively large numerical aperture.

FIGS. 3 a, 3 b, and 3 c illustrate the ray focusing properties ofparabolic, spherical, and elliptical mirrors, respectively, in the planeof the page.

FIG. 4 a is a projected view of a dual-mirror configuration inaccordance with an embodiment of the invention.

FIG. 4 b is a projected view of a second dual-mirror configuration inaccordance with an embodiment of the invention.

FIG. 4 c is a projected view of the first dual-mirror configuration ofFIG. 4 a in a plane perpendicular to the viewing plane as in FIG. 4 a inaccordance with an embodiment of the invention.

FIG. 4 d is a projected view of the second dual-mirror configuration ofFIG. 4 b in a plane perpendicular to the viewing plane as in FIG. 4 b inaccordance with an embodiment of the invention.

FIG. 5 shows a projected view of a two-mirror broadband obliqueilluminator for an optical inspection system in accordance with anembodiment of the invention.

FIG. 6 shows another projected view of the illuminator of FIG. 5 inaccordance with an embodiment of the invention.

FIG. 7 shows ray fan plots of the broadband oblique illuminator of FIGS.5 and 6 in accordance with an embodiment of the invention.

FIG. 8 shows a projected view of a one-piece dual-reflector broadbandoblique illuminator for an optical inspection system in accordance withan embodiment of the invention.

FIG. 9 shows another projected view of the illuminator of FIG. 8 inaccordance with an embodiment of the invention.

FIG. 10 shows ray fan plots of the illuminator of FIGS. 8 and 9 inaccordance with an embodiment of the invention.

FIG. 11 shows a perspective view of an implementation of a one-piecedual-reflecting optical element in accordance with an embodiment of theinvention.

FIG. 12 is an optical layout of a light beam being focused by theoptical element of FIGS. 8 to 11 in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

Previous oblique (non-normal) illuminators have various drawbacks. Onedrawback is that previous oblique illuminators typically use cylindricalmirrors with spherical or aspherical cross-sections which produceresidual aberrations. A corrective element may be introduced to correctfor the residual aberrations, but the correction is generally notcomplete, the residual aberration will limit the increase in numericalaperture. Another drawback is that previous oblique illuminators aretypically sensitive to the wavelength of the illumination. In otherwords, they are effectively narrowband due to wavelength dispersionthrough refractive or dispersive materials. Another drawback is thatprevious oblique illuminators are typically sensitive to misalignment oftheir optical elements. A small misalignment may substantially impacttheir optical performance.

FIG. 1 is an optical system layout of a previous oblique illuminator foruse in inspecting manufactured substrates. Such a previous obliqueilluminator is described in U.S. Pat. No. 7,199,946. This previousoblique illuminator includes a light source 102, a first mirror 104, anda second mirror 106.

The first and second mirrors (104 and 106, respectively) are cylindricalmirrors to form a narrow line beam illumination on the target 108. Theaxes of the cylindrical mirrors are parallel to the lines whichrepresent the mirrors in the diagram. The cylindrical mirror pairproduces residual aberrations. In order to correct for theseaberrations, an aspherical cylindrical element (also called an acylinderelement or an acylindrical element) 110 is introduced between the source102 and the first mirror 104.

In one implementation of the oblique illuminator in FIG. 1, theprojected numerical aperture in a plane normal to the illuminating lineon the target 108 is 0.7, which is somewhat small. It is desirable tohave a higher numerical aperture, such as 0.85, or 0.95, or even higher,to reduce the linewidth of the line illumination. However, if the designdepicted in FIG. 1 is used, then increasing the numerical apertureresults in a dramatic increase in the residual aberrations caused by thecylindrical mirrors. In other words, the aspherical term for theacylinder increases dramatically. Even so, the residual aberrationsstill cannot be completely corrected.

FIG. 2 shows ray fan plots of the oblique illuminator of FIG. 1 with arelatively large numerical aperture of 0.85. The ray fan plots show rayaberrations as a function of pupil coordinate. As seen by the X-FANplots on the right side of FIG. 2, substantial ray aberrations arepresent in the x-dimension. For a numerical aperture of 0.85, theaspheric sag is relatively larger (larger than 2 microns), and extraaspherical terms are needed to reduce the residual aberrations.

FIGS. 3 a, 3 b, and 3 c illustrate the ray focusing properties ofparabolic, spherical, and elliptical mirrors, respectively, in the planeof the page. These diagrams are described to provide a foundation tounderstand the embodiments of the invention disclosed herein.

Per FIG. 3 a, a parallel beam of incident light 304 is reflected fromthe convex surface of the parabolic mirror 302. The rays of thereflected light diverge as if originating from a virtual point source306 behind the mirror 302. The virtual point source 306 is at the focalpoint of the parabolic shape of the mirror surface 302. As such a convexparabolic mirror may form a perfect virtual image at its focal pointwhich is a distance z=R/2 from the vertex of the parabola, where R isthe radius of curvature of the parabola.

If 302 is a cylindrical mirror with a parabolic cross-section, a virtualline image 306 will be formed. As such, a concave parabolic cylindricalmirror may be used to form a perfect virtual line image for a collimatedinput light.

Per FIG. 3 b, incident light from a point source 314 is reflected from aconcave surface of a spherical mirror 312. In the illustrated case, thepoint source 314 is at the center of the spherical shape of the mirrorsurface 312. In this case, the reflected rays converge back onto thepoint source 314. As such, a concave spherical mirror may be used toform a perfect image of an object located at its center.

Similarly, a perfect line image can be formed by placing a line object314 at the center line of a cylindrical mirror 312. As such, acylindrical mirror may be used to form a perfect line image of a lineobject at its center.

Per FIG. 3 c, incident light from a point source is reflected from aconcave surface of an elliptical mirror 322. The point source may be ata first focal point of the elliptical shape of the mirror surface 322.The reflected light converges onto a second focal point of theelliptical shape. The point source may be at the farther focal point324, and the reflected rays may converge at the nearer focal point 326,or vice versa. As such, a concave elliptical mirror may be used to forman image at one focal point of the ellipse when an object is placed atthe other focal point.

Similarly, a perfect line image can be formed at one focal line 326 of aa cylindrical mirror 322 with an elliptical profile by placing a lineobject 324 at the other focal line. As such, a cylindrical mirror withan elliptical profile may be used to form a perfect line image byplacing a line object at one of its focal line.

FIG. 4 a is a projected view of a first dual-mirror configuration inaccordance with an embodiment of the invention. A projected view inanother orientation of this first dual-mirror configuration is shown inFIG. 4 c. This dual-mirror configuration includes a first mirror 404which is a convex parabolic cylindrical mirror and a second mirror 406which is a concave spherical cylindrical mirror.

The first mirror 404 has a reflective convex surface shaped as acylinder where the projected profile of the cylinder is parabolic. InFIG. 4 a, the first mirror 404 is parabolic in the plane of the page,and the axis of the cylinder is normal to the plane of the page. Theparabolic cylinder has a virtual focal line 408 which is normal to theplane of the page.

The second mirror 406 has a reflective concave surface shaped as acylinder where the projected profile of the cylinder is spherical. InFIG. 4 a, the second mirror 406 is spherical in the plane of the page,and the axis 409 of the cylinder is normal to the plane of the page. Inparticular, the axis 409 of the spherical cylinder 406 is coincidentwith the virtual focal line 408 of the parabolic cylinder 404.

A beam of light from a light source 402 reflects from the reflectiveconvex surface of the first mirror 404 to the second mirror 406. Thelight source 402 may be, for example, an ultraviolet wavelength laser.The light is reflected from the reflective concave surface of the secondmirror 406 converges to its axis 409 (which is also the virtual focalline 408 of the first mirror 404). The axis 409 lies on the surface ofthe target substrate 410 such that an illuminated line segment is formedon the target surface.

FIG. 4 b is a projected view of a second dual-mirror configuration inaccordance with an embodiment of the invention. A projected view inanother orientation of this second dual-mirror configuration is shown inFIG. 4 d. This dual-mirror configuration includes a first mirror 414which is a convex parabolic cylindrical mirror and a second mirror 416which is a concave elliptical cylindrical mirror.

The first mirror 414 has a reflective convex surface shaped as acylinder where the projected profile of the cylinder is parabolic. InFIG. 4 b, the first mirror 414 is parabolic in the plane of the page,and the axis of the cylinder is normal to the plane of the page. Theparabolic cylinder has a virtual focal line 418 which is normal to theplane of the page.

The second mirror 416 has a reflective concave surface shaped as acylinder where the projected profile of the cylinder is elliptical. InFIG. 4 b, the second mirror 416 is elliptical in the plane of the page.A first (in this case, nearer) focal line 419 of the elliptical cylinderis normal to the plane of the page. In particular, the first focal line419 of the elliptical cylinder 406 is coincident with the virtual focalline 418 of the parabolic cylinder 414. A second (in this case, farther)focal line 420 of the elliptical cylinder is also normal to the plane ofthe page.

A beam of light from a source 412 reflects from the reflective convexsurface of the first mirror 414 to the second mirror 416. The light isreflected from the reflective concave surface of the second mirror 416converges to the second focal line 420. The second focal line 420 lieson the surface of the target substrate 422 such that an illuminated linesegment is formed on the target surface.

Note that while FIG. 4 b depicts the embodiment where the nearer focalline of the elliptical cylinder is coincident with the focal line of theparabolic cylinder, and where the farther focal line of the ellipticalcylinder is coincident with the surface of the target substrate. Inanother embodiment, the nearer and farther focal lines may be reversed.In other words, in this other embodiment, the farther focal line of theelliptical cylinder is coincident with the focal line of the paraboliccylinder, and the nearer focal line of the elliptical cylinder iscoincident with the surface of the target substrate.

Applicants have determined that the radius of curvature of the convexreflecting and concave reflecting surfaces are independent of the indexof refraction of the medium in between the two reflective surfaces.Hence, in the embodiments described above in relation to FIGS. 4 athrough 4 d, the medium between the two mirrors may be air, or any otherlight-transmitting medium, such as, for example, fused silica, orcalcium fluoride.

In one implementation, where the design may be constructed using twoseparate reflective mirror elements, and the medium may be air. In thisimplementation, each mirror element may include a supporting substratewith a reflective layer on its surface. Such an implementation isdescribed below in relation to FIGS. 5 through 7. In anotherimplementation, the design may be constructed using a singlelight-transmitting solid piece with two reflecting surfaces. Such animplementation is described below in relation to FIGS. 8 through 11.

FIG. 5 shows an optical layout of a two-mirror broadband obliqueilluminator for an optical inspection system in accordance with anembodiment of the invention. A projected view of the illuminator isdepicted in FIG. 6. In addition, a lens listing for this illuminator isprovided in Appendix A. The illuminator depicted in FIGS. 5 and 6includes a light source 502, a first mirror 504, and a second mirror 506which is a separate optical element from the first mirror 504. Themedium between the two mirrors may be air, for example, or any otherlight-transmitting medium, such as, for example, fused silica.

The first (bottom) mirror 504 is a convex parabolic cylindrical mirror(i.e. a convex cylindrical mirror having a projected parabolic profile)with a virtual focus line which lies above (or on) the image plane (i.e.the plane of the target surface). The second (top) mirror 506 is aconcave elliptical cylindrical mirror (i.e. a concave cylindrical mirrorhaving a projected elliptical profile) with a first focus line which iscoincident with the virtual focus line of the first mirror 504 and asecond focus line which lies on the surface of the target substrate 508.

FIG. 7 shows ray fan plots of the two-mirror broadband obliqueilluminator of FIGS. 5 and 6 in accordance with an embodiment of theinvention. As seen in FIG. 7, there is an absence of geometricalaberrations using this illuminator design.

As described previously, the second mirror 506 can be a concavespherical cylindrical mirror, in which case, the virtual focus lineformed by the first mirror 504 lies on the image plane which is thetarget substrate surface 508, the two focal lines of the second mirror506 will overlap and lie on the top surface of the target substrate 508.

In addition to the illuminator, the optical inspection system includes adetector 510 and a processing system 512. The detector 510 may beconfigured to detect light scattered, diffracted, and/or reflected fromthe illuminated line segment on the surface of the target substrate andto generate light-detection signals based on the detected light. Theprocessing system 512 may be configured with electronic circuitry toprocess the light-detection signals from the detector to generate imagedata and a computer (including one or more processors, memory, andcomputer-readable program code) to process the image data to detectdefects on the surface of the target substrate.

FIG. 8 shows a line-spread view of a one-piece dual-reflecting broadbandoblique illuminator for an optical inspection system in accordance withan embodiment of the invention. In this embodiment, the material betweenthe two reflecting surface may not be air and may have a refractiveindex of greater than 1.0, A projected view of this illuminator isdepicted in FIG. 9. In addition, a lens listing for this illuminator isprovided in Appendix B. The illuminator depicted in FIGS. 8 and 9includes a light source 802 and a single-piece (one-piece) dualreflector which includes an entry surface 803, a first reflectingsurface 804, a second reflecting surface 806, and an exit surface 807.The one-piece dual reflector may be made out of a rigidlight-transmitting material, such as glass, which is preferablyinsensitive to thermal variations. This design is substantiallyachromatic and is insensitive to the glass selection.

A light beam emitted from the source 802 enters the one-piece dualreflector at the entry surface 803 and travels to the first (bottom)surface 804. The first surface 804 is a convex parabolic cylindricalsurface (i.e. a convex cylindrical surface with a projected parabolicprofile) with a virtual focus line which lies just slightly above ordirectly on the image plane (i.e. the plane of the target surface). Thelight beam is refracted by the entry surface 803, then reflected fromthe first surface 804 and travels to the second (top) surface 806,finally the light beam refracted again by the exit surface 807 and forma line image on top of the target substrate surface 808. The reflectionfrom the first surface 804 may be by total internal reflection.

The second surface 806 can be a concave spherical surface mirror (i.e. aconcave cylindrical surface with spherical curvature) with a focus linewhich is coincident with the virtual focus line of the first surface 804and which also lies on the surface of the target substrate 808. Notethat a cylindrical surface with a spherical curvature is a special caseof a cylindrical surface with elliptical curvature, where the two focallines of the elliptically-curved cylinder are coincident (i.e. thesame). The light beam is reflected from the second surface 806 andtravels to the target substrate surface 808. The reflection from thesecond surface 806 may be by total internal reflection.

The light beam exits the one-piece dual reflector at the exit surface807 and illuminates a line segment on the surface of the targetsubstrate 808. Note that the entrance surface 803 and exit surface 807are preferably parallel to each other and are preferably normal to theformed line image on the target surface. The oblique (non-normal) angleof illumination may vary depending on the implementation. In onespecific implementation, the illumination may be at an incident angle of64 degrees, where the incident angle of normal illumination is definedas zero degrees.

Similar to the previous embodiment as in FIGS. 5 to 7, the secondsurface 806 can also be an elliptical cylindrical surface, in whichcase, the virtual focal line of the first surface 804 will coincide withone focal line of the second surface 806, while the other focal line ofthe second surface 806 will lie on the top surface of the targetsubstrate 808.

Note that for the one-piece dual reflector there is no need for a mirrorsubstrate to support the bottom reflecting surface. This is because thebottom reflecting surface is a bottom surface of the single piece inthis embodiment. As such, the single-piece optics may be placed veryclose to the image plane (i.e. the plane of the target surface). Usingthis design, a high numerical aperture of 0.9, or 0.95, or even closerto 1.0 may be achievable.

In contrast, an embodiment which requires the bottom mirror to besupported by a mirror substrate may not be positioned so close to theimage plane. Since the incoming light beam has a limited beam width,this would limit the numerical aperture such that high numericalapertures may be difficult to achieve.

The radius of curvature (R₁) of the parabolic cylindrical reflectingsurface 804 satisfies Equation 1.

$\begin{matrix}{R_{1} = {- \frac{\frac{\phi}{2}}{\tan( \frac{\sin^{- 1}N\; A}{2} )}}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$where φ represents the diameter of the incoming beam, and NA is thetarget numerical aperture of the laser line beam.

The radius of curvature (R₂) of the spherical cylindrical reflectingsurface 806 satisfies the Equation 2.

$\begin{matrix}{R_{2} = {\frac{R_{1}}{2} + d}} & ( {{Equation}\mspace{14mu} 2} )\end{matrix}$where d represents the vertical distance between the two reflectingsurfaces.

Applicants have determined that the values of R₁ and R₂ are independentof the index of refraction of the medium between the two reflectivesurfaces. As such, the tolerance on the index of refraction isinsensitive. (In the extreme case, it can be air. However, in the casewhere the medium between the two reflecting surfaces is air, extrasubstrates are needed to support the two reflecting surfaces.)

In addition to the illuminator, the optical inspection system includes adetector 810 and a processing system 812. The detector 810 may beconfigured to detect light scattered, diffracted, and/or reflected fromthe illuminated line segment on the surface of the target substrate andto generate light-detection signals based on the detected light. Theprocessing system 812 may be configured with electronic circuitry toprocess the light-detection signals from the detector to generate imagedata and a computer (including one or more processors, memory, andcomputer-readable program code) to process the image data to detectdefects on the surface of the target substrate.

FIG. 10 shows ray fan plots of the illuminator of FIGS. 8 and 9 inaccordance with an embodiment of the invention. As seen in FIG. 10, aperfect line without geometrical aberration may be formed on the surfaceof the target substrate.

FIG. 11 shows a perspective view of an implementation of a one-piecedual-reflecting optical element in accordance with an embodiment of theinvention. As seen in FIG. 11, the one-piece dual-reflecting opticalelement includes an entry surface 803, a first (bottom) surface 804, asecond surface 806, and an exit surface 807.

Advantageously, this illuminator design is achromatic. As such, thewidth of the spectral band will not affect the linewidth of the finalbeam profile. Applicants have further determined that the line willindeed spread due to the index of refraction variation at differentwavelengths, where the color spread (Δd) along the non-powered directionof the optics on the target substrate plane 808 satisfies Equation 3, asshown in FIG. 12.

$\begin{matrix}{{\Delta\; d} = {{t( {{\tan( {\sin^{- 1}\frac{\sin( {\frac{\pi}{2} - \theta} )}{n_{2}}} )} - {\tan( {\sin^{- 1}\frac{\sin( {\frac{\pi}{2} - \theta} )}{n_{1}}} )}} )}\tan\;\theta}} & ( {{Equation}\mspace{14mu} 3} )\end{matrix}$where t represents the distance between the entrance port (surface) 803and the exit port (surface) 807, and n₁ and n₂ are the indices ofrefraction at the outer extreme wavelengths, and θ is the illuminationincident angle for the light beam 1202 entering the entrance port 803.

One advantage of using the single-piece reflecting design is that, sincethe bottom reflecting surface does not need to have a substrate, thewhole line forming optical piece may be placed very close to the imagingplane, which is the top surface of the target substrate.

If the illumination incident angle θ (as in FIG. 12) is high enough tosatisfy Equation 4, then total internal reflection will occur on the tworeflection surfaces 804 and 806, no reflecting coating is required onthis two surfaces.

$\begin{matrix}{{n\;{\cos( {\sin^{- 1}( \frac{\cos\;\theta}{n} )} )}} > 1} & ( {{Equation}\mspace{14mu} 4} )\end{matrix}$where n is the refractive index for the longest wavelength within theilluminating spectrum.

However, in a lot of cases, the first and second reflecting surfaces(804 and 806, respectively) are still coated with reflective coatings.One advantage is that coating both cylindrical surfaces of the one-pieceoptical element minimizes phase retardation issues related with theimplementation of total internal reflection (TIR) reflections.

Appendix A

Lens Listing for Dual Mirror Design. RDY THI RMD GLA > OBJ: INFINITYINFINITY STO: INFINITY 144.133222 2: INFINITY 0.000000 XDE: 0.000000YDE: 0.000000 ZDE: 0.000000 ADE: −64.000000 BDE: 0.000000 CDE: 0.0000003: INFINITY −19.000000 REFL XTO: RDX: 7.93069 K: −1.000000 A:0.000000E+00 B: 0.000000E+00 C: 0.000000E+00 D: 0.000000E+00 CUM:0.000000 THM: 8.000000 GLM: 4: INFINITY 0.000000 5: INFINITY 30.000000REFL XTO: RDX: 26.01552 K: −0.017640 A: 0.000000E+00 B: 0.000000E+00 C:0.000000E+00 D: 0.000000E+00 XDE: 0.000000 YDE: 38.955773 ZDE: 0.000000ADE: 0.000000 BDE: 0.000000 CDE: 0.000000 CUM: 0.000000 THM: 8.000000GLM: IMG: INFINITY 0.000000 XDE: 0.000000 YDE: 61.509115 ZDE: 0.000000DAR ADE: 0.000000 BDE: 0.000000 CDE: 0.000000 SPECIFICATION DATA EPD15.00000 DIM MM WL 354.80 REF 1 WTW 1 XAN 0.00000 0.00120 YAN 0.000000.00120 WTF 1.00000 1.00000 VUX 0.00000 0.00000 VLX 0.00000 0.00000 VUY0.50000 0.50000 VLY 0.50000 0.50000 POL N INFINITE CONJUGATES EFL0.1000E+19 BFL −0.1000E+19 FFL −0.1000E+19 FNO 0.6667E+17 AT USEDCONJUGATES RED *********** FNO −0.6667E+17 OBJ DIS 0.1000E+14 TT0.1000E+14 IMG DIS 30.0000 OAL 125.1332 PARAXIAL IMAGE HT 0.2094E+14 THI−0.1000E+19 ANG 0.0012 ENTRANCE PUPIL DIA 15.0000 THI 0.0000 EXIT PUPILDIA 15.0000 THI −163.1332

Appendix B

Lens Listing for Single Piece Design. lfc_t2 aut_z4d7e4 73.8 2x RDY THIRMD GLA > OBJ: INFINITY INFINITY 1: INFINITY 0.000000 2: INFINITY130.540062 STO: INFINITY 0.000000 4: INFINITY 0.000000 XDE: 34.960149YDE: 0.000000 ZDE: 108.319408 ADE: 0.000000 BDE: 64.000000 CDE: 0.0000005: INFINITY 0.000000 XDE: 0.000000 YDE: 0.000000 ZDE: 0.000000 ADE:0.000000 BDE: 0.000000 CDE: 0.000000 6: INFINITY 0.000000 XDE:−99.807942 YDE: 0.000000 ZDE: 0.000000 GLB G5 ADE: 0.000000 BDE:0.000000 CDE: 0.000000 7: INFINITY 0.000000 SILICA_SPECIAL XDE: 0.000000YDE: 0.000000 ZDE: 0.000000 DAR ADE: 0.000000 BDE: −90.000000 CDE:0.000000 8: 9.94547 0.000000 TIRO SILICA_SPECIAL GL2: YTO: RDX: INFINITYK: −1.000000 A: 0.000000E+00 B: 0.000000E+00 C: 0.000000E+00 D:0.000000E+00 XDE: −84.341764 YDE: 0.000000 ZDE: −4.972736 GLB G5 ADE:0.000000 BDE: 0.000000 CDE: 0.000000 CEM: CIN: CTH: 0.0000 9: 17.900000.000000 TIRO SILICA_SPECIAL GL2: YTO: RDX: INFINITY K: 0.000000 A:0.000000E+00 B: 0.000000E+00 C: 0.000000E+00 D: 0.000000E+00 XDE:−42.776198 YDE: 0.000000 ZDE: −17.900000 GLB G5 ADE: 0.000000 BDE:0.000000 CDE: 0.000000 CEM: CIN: CTH: 0.0000 10: INFINITY 0.000000 XDE:16.768249 YDE: 0.000000 ZDE: 0.000000 DAR ADE: 0.000000 BDE: 90.000000CDE: 0.000000 11: INFINITY 17.900000 12: INFINITY 0.000000 IMG: INFINITY0.000000 XDE: 42.776198 YDE: 0.000000 ZDE: 0.000000 DAR ADE: 0.000000BDE: 0.000000 CDE: 0.000000 SPECIFICATION DATA EPD 14.40000 DIM MM WL354.80 REF 1 WTW 1 INI SZ XAN 0.00000 YAN 0.00000 WTF 1.00000 VUX0.50000 VLX 0.50000 VUY 0.00000 VLY 0.00000 POL Y PFR 1.0000 PTP 0.0000POR 90.0000 PRO LIN PCS COL PST IDL RVT N REFRACTIVE INDICES GLASS CODE354.80 SILICA_SPECIAL 1.476108 INFINITE CONJUGATES EFL 3.3688 BFL−5.7735 FFL 236.9877 FNO 0.2339 IMG DIS 0.0000 OAL 238.8595 PARAXIALIMAGE HT 0.0000 ANG 0.0000 ENTRANCE PUPIL DIA 14.4000 THI 130.5401 EXITPUPIL DIA 0.4557 THI −5.6669

What is claimed is:
 1. An oblique illuminator comprising: a light sourceemitting a light beam; a first reflective surface having a convexcylindrical shape with a projected parabolic profile which is configuredto reflect the light beam from the light source and which defines afocal line; and a second reflective surface having a concave cylindricalshape with a projected elliptical profile which is configured to reflectthe light beam from the first reflective surface and which defines firstand second focal lines, wherein the focal line of the first reflectivesurface is coincident with the first focal line of the second reflectivesurface, wherein the projected elliptical profile of the secondreflective surface is configured such that the second focal line of thesecond reflective surface lies on a surface of a target substrate, andwherein the light beam reflected from the second reflective surfaceimpinges on the target surface at an oblique angle.
 2. The obliqueilluminator of claim 1, wherein the first and second focal lines are asingle focal line.
 3. The oblique illuminator of claim 1, wherein thefirst and second reflective surfaces each comprise a mirror coating on asupport substrate.
 4. The oblique illuminator of claim 3, furthercomprising an air medium between the first and second reflectivesurfaces.
 5. The oblique illuminator of claim 3, further comprising amedium whose refractive index is greater than 1.0 between the first andsecond reflective surfaces.
 6. The oblique illuminator of claim 1,wherein the first reflective surface comprises a bottom surface of anoptical element, and the second reflective surface comprises a topsurface of the optical element.
 7. The oblique illuminator of claim 6,wherein the optical element is formed of a rigid light-transmittingmaterial, and wherein the first and second reflective surfaces areconfigured to reflect the light beam by total internal reflection. 8.The oblique illuminator of claim 6, wherein the rigid light-transmittingmaterial comprises glass.
 9. The oblique illuminator of claim 6, whereinthe elliptical profile is a spherical profile, and wherein the first andsecond focal lines are a single focal line.
 10. The oblique illuminatorof claim 1, wherein the light source comprises an ultraviolet wavelengthlaser.
 11. A method of illuminating a line on a surface of a targetsubstrate, the method comprising: emitting a light beam from a lightsource; reflecting the light beam from a first reflective surface havinga convex cylindrical shape with a projected parabolic profile whichdefines a focal line; and reflecting the light beam from a secondreflective surface having a concave cylindrical shape with a projectedelliptical profile which defines first and second focal lines, whereinthe focal line of the first reflective surface is coincident with thefirst focal line of the second reflective surface, wherein the projectedelliptical profile of the second reflective surface is configured suchthat the second focal line of the second reflective surface lies on asurface of a target substrate, and wherein the light beam reflected fromthe second reflective surface impinges on the target surface at anoblique angle.
 12. The method of claim 11, wherein the first and secondfocal lines are a single focal line.
 13. The method of claim 11, whereinthe first and second reflective surfaces each comprise a mirror coatingon a support substrate.
 14. The method of claim 13, further comprisingthe light beam traveling through an air medium between the first andsecond reflective surfaces.
 15. The method of claim 13, furthercomprising the light beam traveling through a fused silica mediumbetween the first and second reflective surfaces.
 16. The method ofclaim 11, wherein the first reflective surface comprises a bottomsurface of an optical element, and the second reflective surfacecomprises a top surface of the optical element.
 17. The method of claim16, wherein the optical element comprises a rigid light-transmittingmaterial, and wherein the reflection from the first and secondreflective surfaces is by total internal reflection.
 18. The method ofclaim 16, wherein the rigid light-transmitting material comprises glass.19. The method of claim 16, wherein the first and second focal lines area single focal line.
 20. The method of claim 11, wherein the lightsource comprises an ultraviolet wavelength laser.